A cordless telephone system typically includes a portable cordless handset and a cordless base station connected to a telephone company phone system by telephone landlines. The cordless base station has an assigned landline telephone number that allows the user to place and receive calls using the cordless portable handset within a limited range of the cordless base station, such as in a home. However, due to their limited range, the cordless portable handset provides the user with relatively local radiotelephone communication.
Radiotelephone communication outside the range of the cordless telephone system may also be provided to the user via a cellular telephone system. A cellular telephone system typically includes cellular subscriber units (mobile or portable) and cellular base stations connected to the landline telephone system via one or more cellular switching networks. Each cellular subscriber unit has an assigned cellular telephone number that allows the user to place and receive calls within a widespread range of the cellular base stations, such as throughout a metropolitan area. However, the cost of using the cellular telephone service is much greater than the cordless telephone service.
A problem exists for the user that frequently relocates between the cordless and cellular telephone systems. An incoming call routed to the system where the user is not located may be missed. Thus there exists a need for a system that reroutes a user's telephone calls to the system where the user is located.
Additionally, a portable radiotelephone which transmits and receives calls in both a cellular and a cordless system should have the capability to select the clearest available channel for use. An automatic channel selection should minimize interference and eliminate the need for conventional frequency planning.
A problem exists in selecting a clear channel without losing data or adding cost to either the cordless base station or to the radiotelephone. Thus there exists a need for a system that can select a clear channel without losing data or adding cost to the cordless base station or the radiotelephone.
Additionally, any portable radio device that uses batteries can profit from a system to increase the time period between battery recharging times. Previous solutions in the cellular telephone system rely on messages being repeated for a majority vote error correcting. The radiotelephone turns off its receiver if it correctly decodes the first message or there are no errors in a majority vote of the first three transmissions of the message. The receiver remains off for the remaining repeats of the message. However, this solution requires the system to use majority vote error correcting. Thus there exists a need for a power saving system which does not rely on majority vote error correcting.